The objective of this work was to improve the accuracy of the combustion speed estimation in rich fuel condition (φ ≻ 1.2) as in case of Gasoline Direct Injection (GDI) engine. During rich fuel mixture combustion, the accuracy of calculation of laminar burning velocity deteriorates due to not considering the flame stretch. In the present study, the unstable flame was formed due to the imbalance of the mass diffusion and the temperature diffusion of the fuel (Lewis Number (Le) ≺1.0) was modeled. The laminar burning speed model was developed by considering the stretch. It was applied with three-dimensional combustion simulation tools together with the Universal Coherent Flamelet Model (UCFM), a flame propagation model. The model has shown the capability to reproduce the heat generation (heat release rate) at high accuracy in comparison with experimental data. The simulation was carried out for both homogeneous and the stratification combustion (includes GDI) and validated with experimental data.